US4351659A - Method for manufacture of graded index optical fibres - Google Patents

Method for manufacture of graded index optical fibres Download PDF

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Publication number
US4351659A
US4351659A US06/314,779 US31477981A US4351659A US 4351659 A US4351659 A US 4351659A US 31477981 A US31477981 A US 31477981A US 4351659 A US4351659 A US 4351659A
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body portion
glass
flow tube
crucible
temperature
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Keith J. Beales
Clive R. Day
George R. Newns
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Assigned to BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY reassignment BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY THE BRITISH TELECOMMUNICATION ACT 1984. (APPOINTED DAY (NO.2) ORDER 1984. Assignors: BRITISH TELECOMMUNICATIONS
Assigned to BRITISH TELECOMMUNICATIONS reassignment BRITISH TELECOMMUNICATIONS THE BRITISH TELECOMMUNICATIONS ACT 1981 (APPOINTED DAY) ORDER 1981 (SEE RECORD FOR DETAILS) Assignors: POST OFFICE
Assigned to BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY reassignment BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY THE BRITISH TELECOMMUNICATIONS ACT 1984. (1984 CHAPTER 12) Assignors: BRITISH TELECOMMUNICATIONS
Assigned to BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY reassignment BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY THE TELECOMMUNICATIONS ACT 1984 (NOMINATED COMPANY) ORDER 1984 Assignors: BRITISH TELECOMMUNICATIONS
Assigned to BRITISH TELECOMMUNICATIONS reassignment BRITISH TELECOMMUNICATIONS THE BRITISH TELECOMMUNICATIONS ACT 1981 (APPOINTED DAY) ORDER 1981 (SEE RECORD FOR DETAILS) Assignors: POST OFFICE
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
    • C03B37/022—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from molten glass in which the resultant product consists of different sorts of glass or is characterised by shape, e.g. hollow fibres, undulated fibres, fibres presenting a rough surface
    • C03B37/023—Fibres composed of different sorts of glass, e.g. glass optical fibres, made by the double crucible technique
    • C03B37/0235—Thermal treatment of the fibre during the drawing process, e.g. cooling
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2205/00—Fibre drawing or extruding details
    • C03B2205/56—Annealing or re-heating the drawn fibre prior to coating

Definitions

  • the present invention relates to improvements in double crucibles for use in the manufacture of graded index optical fibre, improvements in apparatus for use in the production of graded index optical fibre, and improved methods of manufacture of graded index optical fibre.
  • a graded index optical fibre we mean a fibre wherein the refractive index varies gradually from the centre of the fibre to radially outer positions.
  • the radial refractive index variation may be produced by subjecting the fibre which inherently comprises separate radially inner and outer parts (core and cladding) to thermal diffusion whereby the interface between the parts and the discrete change in refractive index is converted by the application of heat to a mixed region and a gradual change in refractive index.
  • the diffusion effect should extend to the centre of the core and to a position radially outwardly of the junction between the core and cladding.
  • the optical fibre should be subjected to a heat treatment such that the quantity Dt/a 2 , generally referred to as ⁇ , lies within the range of from 0.06 to 0.085, where D is the diffusion coefficient governing inter-diffusion between core and cladding, t is the duration of heat treatment, and a is the core radius; see British Pat. No. 1,460,333. It should be noted that even given the optimum value of ⁇ , the refractive index profile obtained is only an approximation to the ideal profile for a graded index optical fibre.
  • the time for which the two glasses are in contact at high temperature is controlled by the rate of flow of glass in through the cladding nozzle. If the flow is increased by raising the temperature, D is increased but t is reduced, resulting in little change in ⁇ . Any change will depend on the relative temperature dependence of D and of the glass viscosity. Large core graded index optical fibres are difficult to make in some glass systems with a value of ⁇ as large as 0.08. It is therefore desirable to increase D in a manner which does not significantly increase the flow of glass in the cladding nozzle.
  • a double crucible for the manufacture of graded index optical fibres, which double crucible comprises an outer body portion for holding molten cladding glass, an inner body portion, within the outer body portion, for holding molten core glass, the inner body portion having an exit orifice leading into the outer body portion, means for maintaining the said body portions at an elevated temperature, and means for extending the dwell period in which the core and cladding glasses remain in contact under diffusing conditions with one another in the crucible.
  • the means for extending the dwell period preferably involve providing on the outer body portion downstream of the exit orifice an elongate flow Zube provided with means for maintaining it at a temperature above that of the said body portions.
  • the invention further provides apparatus for manufacturing graded index optical fibres, which apparatus includes a double crucible as defined in the previous paragraph.
  • the length of the flow tube through which the fibre exits is substantial compared to the length of a conventional drawing nozzle so as to be sufficient to achieve the desired thermal diffusion between the core and cladding.
  • Means may be provided for varying, especially lowering, the temperature of one region of the flow tube between the crucible body and the drawing nozzle, so that the flow rate of molten glass through the tube can be controlled.
  • a cold finger i.e. a cooled element usually having cooling liquid flowing through it and placed adjacent a short region of the tube may be used to provide a lower-temperature region in that region.
  • Cooling means for example, a cold finger, may also be provided adjacent to the drawing nozzle to control the drawing temperature of glass emerging from the nozzle.
  • a method of manufacturing a graded index optical fibre by drawing a clad fibre from a double crucible, in which the inner crucible contains a core glass and the outer crucible contains a cladding glass, in which method, prior to drawing the optical fibre, molten core glass surrounded by and in contact with molten cladding glass is held in this contact for an extended period thereby achieving the desired diffusion characteristics.
  • the glasses pass through an elongate flow tube at least a portion of which is maintained at a temperature higher than the temperature of the double crucible.
  • a region of the said flow tube may be maintained at a temperature which can be varied to permit control of the flow rate of glass through the flow tube. This allows the flow rate to be decreased thereby increasing the dwell time in which thermal diffusion takes place.
  • the apparatus shown in the drawing consists of a double crucible indicated generally by the reference numeral 1, having an inner body portion or inner crucible 2 and an outer body portion or outer crucible 3. Attached to the outer crucible 3 is a flow tube 4 which is relatively long compared with the nozzles usually attached to double crucibles.
  • the body portions of the double crucible are heated by means of 10% platinum-rhodium alloy windings 5 mounted on an alumina winding former 6.
  • the flow tube 4 is surrounded by a silica liner 7.
  • the silica liner is surrounded by a heating element 8 comprising 10% platinum-rhodium wire wound on an alumina winding former.
  • the windings are surrounded by thermal insulation material 9 of suitable form.
  • Reference numeral 10 represents a drawing nozzle which is merely the end of the flow tube 4 from which the optical fibre is drawn.
  • a cold finger 11 may be provided adjacent the drawing nozzle 10 to control the drawing temperature of glass emerging from the nozzle 10.
  • the cold finger 11 consists of watercooled copper coils.
  • a typical double crucible according to the present invention will have an outer crucible diameter A of 60-62 mm and an inner crucible diameter B of 18 mm; angle C on the outer crucible will be 45°, and angle D on the inner crucible will be 55°; the nozzle on the inner crucible will have a diameter E of 2 mm; the flow tube will have a diameter of 31/2 mm, and the length of the flow tube G will be 300 mm. These dimensions are quoted by way of example only.
  • the inner crucible 2 is filled with a glass which is to be used for the core of the optical fibre
  • the outer crucible 3 is filled with a glass which is to be used as the cladding of the optical fibre.
  • Both these glasses may, for example, be suitable soda-boro-silicate glasses such as those described in our U.K. Pat. No. 1,507,711 or, advantageously, one or both may be an alkaline-earth-oxide-modified soda-boro-silicate glass as described in our published E.P.C. Specification No. 0000282.
  • the body portions 2 and 3 of the double crucible are maintained at a temperature within the range of from 900° to 950° C., at which temperature the glasses are of course molten.
  • the flow tube 4 is heated independently of the body portions of the double crucible, and is maintained at a temperature which may be up to 100° C. higher than the crucible body. Increasing the temperature of the molten glass in the flow tube, and lengthening the flow tube, can enhance diffusion by a factor of up to ten on large core fibres.
  • molten glass from the inner and outer crucibles 2 and 3 passes into the flow tube 4.
  • the molten glass then passes through the flow tube 4 relatively slowly.
  • the glass in the flow tube consists of an inner core of core glass, surrounded by cladding glass.
  • the glass necks down into a fibre as it is drawn off using suitable drawing apparatus.
  • the use of a long flow tube 4 increases the duration of the heat treatment during which thermal diffusion occurs, and the enhanced temperature of the flow tube 4 ensures an increased diffusion rate, since the diffusion coefficient increases with temperature.
  • the actual drawing nozzle 10 should preferably be maintained at a temperature which is not substantially different from that of the body of the double crucible. If the temperature of the drawing nozzle is too high, flow instabilities can result which will cause diameter variations in the fibre.
  • the maximum temperature difference between the flow tube 4 and the main body of the crucible can be determined by experiment. If too high a temperature is used for the flow tube, this will create control problems for the temperature of the main crucible.
  • the refractive index profile which is closest to optimum is obtained when ⁇ is within the range of from 0.06 to 0.085; values of ⁇ less than this are caused by under-diffusion of the fibre and values of ⁇ greater than this are caused by over-diffusion of the fibre.
  • the basic problem which this invention seeks to overcome is that arising from under-diffusion, i.e. inadequate diffusion of molten glass between the core and cladding. This is a problem which occurs principally with large core optical fibre, that is to say, fibres having core diameters within the range of from 50 to 70 ⁇ .
  • the measures described and particularly the elongation of tube 4 and the flow control measures described hereinafter increase the period during which the core and cladding glasses are in diffusing contact with one another.
  • the flow rate of glass through the flow tube 4 can be controlled by controlling the rate at which fibre is pulled from the drawing nozzle 10, and also by providing a short portion in the flow tube where a lower temperature is maintained.
  • the use of a short lower temperature region such as indicated at 11 has the effect of introducing a large flow resistance, while not having an appreciable effect on the total diffusion.
  • the intermediate cool region in the flow tube can, for example, be provided by use of a cold finger such as indicated at 11 and provided by a water filled copper coil.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)
  • Glass Melting And Manufacturing (AREA)
US06/314,779 1978-03-14 1981-10-26 Method for manufacture of graded index optical fibres Expired - Lifetime US4351659A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1001678 1978-03-14
GB100161/78 1978-03-14

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US06019161 Division 1979-03-09

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US4351659A true US4351659A (en) 1982-09-28

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US06/314,779 Expired - Lifetime US4351659A (en) 1978-03-14 1981-10-26 Method for manufacture of graded index optical fibres

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US (1) US4351659A (fr)
EP (1) EP0004183B1 (fr)
JP (1) JPS54151631A (fr)
CA (1) CA1095224A (fr)
DE (1) DE2960800D1 (fr)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4439008A (en) * 1981-06-26 1984-03-27 U.S. Philips Corporation Optical fiber of the graded index type and method of producing same
US4452508A (en) * 1977-06-28 1984-06-05 British Telecommunications Graded index optical fibres
US5403536A (en) * 1992-06-19 1995-04-04 Seiki Kabushiki Kaisha Method for injection molding of polyethylene terephthalate resin
US5879426A (en) * 1996-08-12 1999-03-09 The United States Of America As Represented By The Secretary Of The Navy Process for making optical fibers from core and cladding glass rods
US6029475A (en) * 1998-06-30 2000-02-29 Lightpath Technologies, Inc. Batching of molten glass in the production of graded index of refraction glass bodies
US6062047A (en) * 1995-04-19 2000-05-16 Corning Incorporated Device for manufacturing a rod of a material having a cross-sectional composition gradient
KR20010066805A (ko) * 1999-05-27 2001-07-11 루센트 테크놀러지스 인크 플라스틱 광섬유 제조공정
US6279352B1 (en) * 1999-12-30 2001-08-28 Corning Incorporated Long hot zone furnace element and optical fiber drawing method practiced therewith
US6550279B1 (en) 2000-09-01 2003-04-22 Corning Incorporated Process for drawing optical fiber from a multiple crucible apparatus with a thermal gradient
US6588235B2 (en) 2001-08-30 2003-07-08 Corning Incorporated Method of centering a fiber core in a multiple-crucible method
US20030205064A1 (en) * 2000-09-01 2003-11-06 Viatcheslav Artiouchenko Optical fiber and method of producing

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT1179876B (it) * 1984-12-18 1987-09-16 Cselt Centro Studi Lab Telecom Apparecchiatura per la produzione continua di fibre ottiche
US6739155B1 (en) * 2000-08-10 2004-05-25 General Electric Company Quartz making an elongated fused quartz article using a furnace with metal-lined walls
CN105060700B (zh) * 2015-08-07 2018-01-12 中国科学院上海光学精密机械研究所 软玻璃光纤预制棒制作装置及方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3726656A (en) * 1969-10-14 1973-04-10 Pilkington Brothers Ltd Method of producing elongated,clad glass member
US4040807A (en) * 1974-07-10 1977-08-09 The Post Office Drawing dielectric optical waveguides
US4145200A (en) * 1977-01-27 1979-03-20 Nippon Sheet Glass Co., Ltd. Production of optical glass fibers

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1194386A (en) * 1967-10-04 1970-06-10 Ass Elect Ind Improvements in the Extrusion of Glass
US3941474A (en) * 1968-03-15 1976-03-02 Nippon Selfoc Kabushiki Kaisha Light-conducting glass structures
GB1328612A (en) * 1972-01-04 1973-08-30 Standard Telephones Cables Ltd Optical fibre manufacture

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3726656A (en) * 1969-10-14 1973-04-10 Pilkington Brothers Ltd Method of producing elongated,clad glass member
US4040807A (en) * 1974-07-10 1977-08-09 The Post Office Drawing dielectric optical waveguides
US4145200A (en) * 1977-01-27 1979-03-20 Nippon Sheet Glass Co., Ltd. Production of optical glass fibers

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4452508A (en) * 1977-06-28 1984-06-05 British Telecommunications Graded index optical fibres
US4439008A (en) * 1981-06-26 1984-03-27 U.S. Philips Corporation Optical fiber of the graded index type and method of producing same
US5403536A (en) * 1992-06-19 1995-04-04 Seiki Kabushiki Kaisha Method for injection molding of polyethylene terephthalate resin
US6062047A (en) * 1995-04-19 2000-05-16 Corning Incorporated Device for manufacturing a rod of a material having a cross-sectional composition gradient
US5879426A (en) * 1996-08-12 1999-03-09 The United States Of America As Represented By The Secretary Of The Navy Process for making optical fibers from core and cladding glass rods
US6021649A (en) * 1996-08-12 2000-02-08 The United States Of America As Represented By The Secretary Of The Navy Apparatus for making optical fibers from core and cladding glass rods with two coaxial molten glass flows
US6029475A (en) * 1998-06-30 2000-02-29 Lightpath Technologies, Inc. Batching of molten glass in the production of graded index of refraction glass bodies
KR20010066805A (ko) * 1999-05-27 2001-07-11 루센트 테크놀러지스 인크 플라스틱 광섬유 제조공정
US6279352B1 (en) * 1999-12-30 2001-08-28 Corning Incorporated Long hot zone furnace element and optical fiber drawing method practiced therewith
US6550279B1 (en) 2000-09-01 2003-04-22 Corning Incorporated Process for drawing optical fiber from a multiple crucible apparatus with a thermal gradient
US20030205064A1 (en) * 2000-09-01 2003-11-06 Viatcheslav Artiouchenko Optical fiber and method of producing
US6588235B2 (en) 2001-08-30 2003-07-08 Corning Incorporated Method of centering a fiber core in a multiple-crucible method

Also Published As

Publication number Publication date
CA1095224A (fr) 1981-02-10
JPS54151631A (en) 1979-11-29
DE2960800D1 (en) 1981-12-03
EP0004183B1 (fr) 1981-09-16
JPS6221737B2 (fr) 1987-05-14
EP0004183A1 (fr) 1979-09-19

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